The invention relates to a device for injection moulding of plastics, with a plasticizing and injection unit that is provided with at least one electrical drive system for turning a plasticizing screw and for injecting the plasticized plastics material between the mould halves, wherein the injection moulding device is provided with at least one additional drive unit that moves a machine part firstly in a linear manner and subsequently presses it against a fixed stop.
The primary advantage of such devices is in that an electrical drive system is easy to control and adjust, which is advantageous for the actual functioning of the injection moulding device, namely plasticizing and injecting of the plastics material, and lastly the manufacture of items with accurately defined characteristics.
Normally, in the case of a machine with electrical driving of the plasticizing and injection unit, all movements of machine parts are enabled by electric motors. This is based on the advantage of being able to eliminate hydraulic pumps along with the associated connecting hoses and possibilities of leakage. On the other hand, it is clear that the use of an electric motor does not represent the ideal solution for the task of firstly moving a machine part in a linear manner and subsequently pressing it against a fixed stop.
On the one hand, the invention avoids the disadvantages associated with hydraulic drive systems, and on the other hand the use of electric motors for manufacturing a non-critical value pressing force of a stationary part, in that it is provided that the additional drive unit is configured as a pneumatically actuated piston-cylinder unit, and the force exerted by the pistons assumes different values according to the setting of the pistons at a given gas pressure.
The main instance of application of the invention is the use of the pneumatic drive system provided with adjustable translation for pressing the plasticizing and injection unit against the mould halves carried by the stationary die platen. With small machines that operate with low closing pressure, it is also conceivable, however, to actuate the closing unit pneumatically, avoiding electrical and hydraulic drive systems. In any case, however, this is recommended for actuating the ejecting device and the die platen device that both operate with forces that can be achieved with commercially available pneumatic drive systems.